1. Field of the Invention
The present invention relates to a transparent composition formed from an associated product dispersion of an amphiphilic or amphiphatic substance having a high safety factor, such as lecithin, and an external treatment composition containing the same. More specifically, it relates to a novel composition having an excellent transparency, stability with a lapse of time, and safety, and formed from a dispersion of an associated product obtained by mixing an amphiphilic substance having a high safety factor, such as lecithin, and a small amount of a surfactant as the solubilizing aid, and an external treatment composition containing the same.
2. Description of the Related Art
Many effective substances, physiologically active substances, and skin drugs are oily substances, and there is a need to develop a transparent system base by which they can be stably formulated. In the prior art, to obtain a transparent system having an oily component formulated therein, a method is known in which a surfactant or ethanol is formulated at a high concentration, but the formulation of these components at a high concentration sometimes causes irritation to the skin, eyes, and mucosa.
To reduce this irritation, a method is known of using lecithin with a high safety factor, which is derived from a natural product, instead of synthetic surfactants, but lecithin has a weak emulsifying power and solubilizing power, and therefore, a highly transparent system cannot be obtained. Further, the system has a poor stability. Also, to increase the transparency by reducing the particle size, a method is known in which, for example, a high pressure emulsifier is used, but in this method, although the transparency immediately after preparation is increased, the stability is poor and the transparency cannot be maintained, and therefore, this method is not practically useful in most cases.
As mentioned above, since lecithin alone cannot provide a required stability, a method is known in which a certain nonionic surfactant or ethanol is used in combination with the lecithin, but to obtain a completely transparent system, a large amount of the nonionic surfactant or ethanol must be used relative to the amount of lecithin used. Further, to enable another oily component to be co-present, the amounts of the nonionic surfactant and ethanol are further increased, whereby irritation again becomes a problem as in the prior art.
Therefore, although methods of obtaining stable transparent systems in which oily components are formulated are known, none of these methods has proved to be successful in practical application.